Phosphate transferring enzymes are of special importance in their role of equilibrating phosphate among the various compounds. This is especially so in growing and contractile cells where there is a high rate of energy turnover. The general research goal is the elucidation of the structure, mechanism of action and role in the cell of the phosphyoryl transferring enzyme, adenylate kinase which catalyzes the reaction: MgATP plus AMP reversibly yields MgADP plus ADP. The enzyme from a variety of sources has and is being purified and properties determined. A molecular model of porcine adenylate kinase derived from X-ray diffraction at 3A resolution is available. An ATP affinity label is being used to identify the ATP subsite. The involvement of amino acid residues at the active site cleft is being determined by chemical modification followed by purification on affinity column and studies of the catalytic and physical properties including NMR where appropriate. Structural and dynamic aspects of the conformation of porcine adenylate kinase will be examined by isotopic exchange and optical methods.